(Elasmobranchii: Carcharhiniformes) in the Pliocene of the Mediterranean Sea
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N. Jb. Geol. Paläont. Abh. 295/2 (2020), 129–139 Article E Stuttgart, February 2020 The extinct catshark Pachyscyllium distans (PROBST, 1879) (Elasmobranchii: Carcharhiniformes) in the Pliocene of the Mediterranean Sea Alberto Collareta, Marco Merella, Frederik H. Mollen, Simone Casati, and Andrea Di Cencio With 4 figures and 1 table Abstract: Sharks assigned to the carcharhiniform family Scyliorhinidae account for about 160 extant species placed in 18 genera. Most living scyliorhinids are small- to medium-sized ground sharks provided with cat- like eyes and nasal barbels similar to whiskers; hence their vernacular name, “cat- sharks”. Living catsharks mostly inhabit deep or rather deep waters of the warm and temperate seas worldwide, foraging on small fishes and inverterbates. In the present paper, we report on a lateral tooth of Scyliorhinidae collected from a clay pit at Certaldo (central Italy), where marine mudstones belonging to the famously fossiliferous Pliocene successions of Tuscany are exposed. This catshark specimen represents the second bona fide record of the extinct premontreine species Pachyscyllium distans in the Pliocene of the Mediterranean Sea, as well as the geologically youngest confirmed occurrence of this species worldwide. In the Mediterranean Pliocene, P. distans thus coexisted with the similar but distinct species Pachyscyllium dachiardii. After having been widespread in Northern Atlantic, Paratethyan, and Mediterranean waters in Miocene times, P. distans became confined to the Mediterranean Sea during the Pliocene. Therefore, similar to what has recently been suggested for P. dachiardii, we hypothesise that the range of P. distans contracted southward as colder conditions took hold in the Northern Hemisphere. The eventual extinction of P. distans might be related to the first cooling episode that significantly affected the Mediterranean biota around 3 Ma. Key words: Chondrichthyes, Scyliorhinidae, Premontreinae, Valdelsa Basin, blue clays, Tuscany, climate change, palaeobiogeography, palaeoichthyology. 1. Introduction deep or rather deep waters (Cappetta 2012). Extant catsharks feed mostly on invertebrates and small fish- The carcharhiniform family Scyliorhinidae includes es; however, the life histories of several living scylio- around 160 living species placed in 18 genera (Weig- rhinid species are still very poorly known (Compagno mann 2016; White et al. 2019); as such, it represents 1984). one of the largest living families of sharks. Most ex- For almost two centuries, the Pliocene marine suc- tant scyliorhinids are small- to medium-sized (i.e., less cessions of Tuscany (central Italy) have been the lo- than 1.5 m in total length) ground sharks that exhibit cation of important finds of fossil remains of elasmo- lengthened, cat-like eyes and, sometimes, whisker- branchs (e.g., Lawley 1876), mostly shark teeth and like nasal barbels (Compagno 1984; Cappetta 2012); batoid dental plates and dermal spines (Marsili 2006, hence their vernacular name, “catsharks”. They inhabit and references therein). These fossils were collected seabottoms in tropical and temperate seas all over the to form important palaeontological collections, such world, ranging from very shallow, marginal-marine ar- as the famous “Lawley collection” (Manganelli et al. eas to depths of more than 2000 m (Compagno 1984). 2006), which was studied (in the past) by illustrious That said, most of the Recent scyliorhinids live in naturalists (e.g., Bassani 1901; De Stefano 1909). © 2020 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/njgpa/2020/0877 0077-7749/2020/0877 $ 2.75 eschweizerbart_xxx 130 A. Collareta et al. Fig. 1. Location of Certaldo, the locality where the fossil scyliorhinid tooth GAMPS-00924 was found (black star), and schematic regional geological map. B-CI = Baccinello-Cinigiano Basin; CA = Casino Basin; RD = Radicofani Basin; SI = Siena Basin; VC = Val di Chiana Basin; VE = Valdelsa Basin; VO-RA-CH = Volterra-Radicondoli- Chiusdino basins. Mod- ified afterMartini et al. (2013) and Spadini & Manganelli (2015). Following the emergence of modern palaeontologi- 2. Stratigraphic framework cal research standards, however, these historical col- lections have lost some of their scientific importance The scyliorhinid fossil tooth described herein was dis- due to widespread uncertainties regarding their geo- covered by one of the authors (S.C.) at an abandoned graphical and stratigraphic context (Landini 1977; quarry at the periphery of the Certaldo village (Flor- Cigala Fulgosi et al. 2009; Collareta et al. 2016). ence Province, Tuscany, central Italy) (Fig. 1). The Now however, the recent reports of rare and elusive GPS geographic coordinates of our find are the fol- elasmobranch taxa from the Pliocene deposits of lowing: 43° 34′ 08″ N; 11° 01′ 51″ E. Tuscany (Spadini & Manganelli 2015; Collareta The fossil specimen was collected from deposits et al. 2017a; Collareta et al. 2017b; Collareta et al. belonging to the Argille Azzurre Formation, a litho- 2018; Manganelli & Spadini 2019), as well as the stratigraphic unit that largely consists of mostly mas- discovery of new fossil localities that are rich in shark sive, shelf mudstones (hence their formational name, and ray teeth (Bianucci et al. 2019), are contributing meaning ‘blue clays’), whose deposition in this area to shed new light on the late Neogene cartilaginous is referred to the Pliocene (Costantini et al. 2004). fish faunas of the Mediterranean Sea. According to Benvenuti et al. (2014), in the Valdelsa In the present paper, on the basis of a single lateral Basin, an intraformational unconformity divides the tooth collected from Pliocene marine mudstones ex- Argille Azzurre Formation into ‘lower’ and ‘upper’ posed at the locality of Certaldo (Tuscany), we provide blue clays, dated to the basalmost Zanclean and upper the second unambiguous record of the extinct catshark Zanclean – lower Piacenzian, respectively. The suc- species Pachyscyllium distans (Scyliorhinidae: Pre- cession exposed at Certaldo belongs to the upper blue montreinae) from the Pliocene of the Mediterranean clays (= ‘upper Argille Azzurre’ of Nalin et al. 2016) Sea and briefly discuss its palaeobiogeographical sig- and can be referred to the S3 Synthem recognised in nificance. the Valdelsa Basin by Benvenuti et al. (2014). The S3 eschweizerbart_xxx Pachyscyllium distans 131 Fig. 2. The Pliocene deposits exposed at the abandoned Certaldo quarry. A – General view of the outcrop. B – Collection of fossil invertebrate and vertebrate remains at the base of the partly revegetated artificial cliff (white arrow). C – Close- up view on a fossil- rich horizon cropping out a couple of meters below the top of the cliff. Synthem is a large-scale depositional sequence that sis spp.) have been calibrated to 3.98 and 3.19 Ma, re- consists of a coarse- grained, deepening-upward delta spectively (Violanti 2012). front stratal package, overlain by a fine- grained divi- At the study site, strata belonging to the Argille Az- sion from an open shelf setting (Dominici et al. 2018). zurre Formation crop out along a partly revegetated The latter comprises a rather monotonous mudstone artificial cliff (Fig. 2A). The succession exposed at the succession that, in the study area, features several Os Certaldo quarry is mostly comprised of substantially trea- and Serpulorbis-rich shell beds (Dominici et al. structureless, greyish- bluish mudstones that host com- 2018). mon remains of macro-invertebrates and erode in a According to Benvenuti et al. (2014), the mud- badland- like fashion (Fig. 2B). Fossils concentrate in stones belonging to the S3 Synthem bear planktonic a ca. 25-cm-thick horizon (Fig. 2C) that also feature foraminifer assemblages indicative of the Mediter- rare invertebrate vertical burrows; this interval runs ranean Pliocene (MPL) zone 4 of Cita (1975) and subhorizontally a couple of meters below the top of the Sprovieri (1992), whose bounding bioevents (i.e., the cliff. The invertebrate assemblage detected at the study last common occurrence of Globorotalia margaritae site includes several species of bivalve and gastropod and the last appearance datum of Sphaeroidinellop molluscs (Bathytoma cataphracta, Calcarata calcara eschweizerbart_xxx 132 A. Collareta et al. Fig. 3. GAMPS-00924, lateral tooth of Pachyscyllium distans (Probst, 1879) from Certaldo (Tuscany, central Italy). A – Lingual view; B – distal view; C – apical view; D – mesial view; E – labial view. ta, Pelecyora brocchii, Petaloconchus intortus, Tena Pachyscyllium distans (Probst, 1879) godus obtusus, and Thylacodes arenarius, among oth- Figs. 3, 4 ers) and a single species of acorn barnacle (Concavus concavus). Vertebrate fossils from the Certaldo quarry Synonymy: See Reinecke et al. (2011: 52), where this spe- include the scyliorhinid specimen studied herein, as cies is referred to as Premontreia (Oxyscyllium) distans well as a few other teeth of elasmobranchs (assigned (Probst, 1879); for an updated list of synonyms and other to Megascyliorhinus miocaenicus and Rostroraja sp.) selected references, include also: and indeterminate otoliths. Most of these remains, in- ?1949 Scyliorhinus guttatum Probst, 1879. – Bauzá cluding the specimen described herein, lack a precise Rullán, p. 208, pl. 15, figs. 1, 2. stratigraphic position; they rolled down from the eas- 1953 Scylliorhinus (= Scyllium) sp. – Bauzá Rullán, ily erodible cliff to accumulate at its base (Fig. 2B). p. 5 (in part), figs. 7–14. 1976